1. Field of the Invention
The present invention relates generally to devices which control the charge stored at a capacitive load by controlling the application of a supply voltage to the load and, more particularly, to a minimum power piezoelectric actuator circuit that quickly and efficiently charges an actuator output voltage in response to an input signal.
2. Discussion of Related Art
Piezoelectric actuators are often used to effect small, but well-controlled displacements of physical objects, such as optical components and machining tools. These mechanical displacements must be very precise and controlled, and are typically on the order of 1-100 microns. In operation, the actuator functions based on an applied voltage. The actuator itself is a capacitor used to store a potential which drives the mechanical displacement. Since capacitors draw no DC current, the theoretical power necessary for actuator operation is very low.
Despite the low power requirements of the actuator, the conventional circuits used to drive piezoelectric actuators unnecessarily dissipate significant power in a number of ways. First, the conventional systems often use power supplies having a voltage higher than is necessary to charge the actuator. These high-voltage power supplies are often separate from other subsystems and dedicated specifically to driving the piezoelectric actuator, resulting in waste and increased manufacturing costs. The conventional piezoelectric actuator systems also typically use resistive elements in portions of the system with significant current flows, thereby causing unnecessary dissipation of power. Furthermore, the conventional circuits used to drive piezoelectric actuators often draw current even when it is not needed to charge the actuator.
In addition to being very precise and accurate, the mechanical displacements effected by a piezoelectric actuator must be well-controlled in the sense that they are properly timed. A piezoelectric actuator must therefore be able to respond quickly to an input drive signal used to control the charging of the actuator. However, many conventional load charging circuits are unable to provide the fast response times required for piezoelectric actuation.
In view of the foregoing, it is an object of the present invention to provide a piezoelectric drive circuit that quickly responds to an input signal and that employs a low voltage power supply and low impedance and reactive components to avoid unnecessary power dissipation. Power is also conserved by drawing current only when necessary to charge the piezoelectric actuator. It is also an object of the present invention that these power saving advantages allow a piezoelectric drive circuit as taught herein to be incorporated into small, portable devices which run on battery power.